1. Field of the Invention
The invention relates to waste-gas piping for a melting furnace, in particular a filter dust melting furnace, which comprises a furnace vessel which is made of fireproof material and is provided, at least in the region of the furnace top, with a thermal insulation, the waste gases occurring in the interior of the furnace being conducted outward through a waste-gas line in the furnace top, a quench being provided in the course of the waste-gas line for the abrupt cooling of the waste gas by cold quenching air acting on it.
Waste-gas piping of this generic type is described in the company's publication "Die thermische Reststoffbehandlung nach dem DEGLOR-Verfahren" [The thermal treatment of residues according to the DEGLOR method] by ABB W+E Umwelttechnik, CH-8048 Zurich, undated.
2. Discussion of Background
In the DEGLOR method (DEGLOR is a registered trade mark of the company W+E Umwelttechnik AG, CH-8048 Zurich), filter dust and boiler ash are treated without additives in an electrically heated melting furnace at temperatures of about 1300.degree. C. The residues melt and are discharged from the furnace via a gas-tight syphon and then cooled. During this process, a glass-like residue occurs which can be disposed of without difficulty. During the melting operation, most of the heavy-metal compounds evaporate. Organic pollutants, such as dioxins or furans are destroyed thermally. Non-evaporating, high-boiling metal compounds are incorporated in the glass matrix in a similar manner to lead in lead crystal glass. A ventilator connected downstream of the furnace ensures that the evaporated components are extracted from the furnace.
This waste gas is cooled abruptly at the furnace outlet to values of about 150.degree.-200.degree. C. The new formation of dioxins can thus be prevented. Additionally, the heavy metal compounds still contained in the waste gas condense or desublimate. Said compounds are subsequently separated from the gas flow in a bag filter and are disposed of separately. The non-condensing gas components (CO2, SO2, HCl, . . . ) are fed, together with the quenching air, back into the furnace chamber of the refuse incineration or into the smoke gas cleaning plant.
Hitherto, plants of this type could not be operated without regular cleaning of the waste-gas pipe in the region between the outlet from the melting furnace and the place where the cold air is blown in (quench). Deposits caused by condensate even form in the quench itself. The removal of these deposits is time-consuming and can only be automated at considerable expense (Swiss Patent 677739).